Although we know a good deal about the structure and function of many structural macromolecules, there is very little understanding of the manner in which the production of such macromolecules is regulated. An appropriate balance between synthesis and degradation is crucial in connective tissues because the tolerance, consistent with normal function, for matrix components is small. This is due, in part, to the slow metabolic turnover of connective tissue proteins in the adult and to the resulting tendency of changes to become cumulative with time. Since we now know that structural macromolecules, in addition to their mechanical-protective roles, also function in sensitive cell-matrix interactions to instruct cellular activity during tissue development and repair, the need for careful regulation of matrix production becomes even more clearcut. The proposed experiments focus on the regulation of type I collagen synthesis by fibroblasts in culture and in cell-free translation systems because this protein is a major constituent of most connective tissues and because pathways for its synthesis and secretion have been elucidated. Model regulatory processes that act at the level of transcription (viral transformation and tumor promoters) and at the level of translation (feedback regulation by procollagen-derived fragments) will be examined. Levels of protein synthesis as well as messenger RNA levels (assessed by cell-free translation and hybridization using cloned cDNA probes for types I and III collagens) will be determined. Fibroblasts from patients with heritable disorders of connective tissues in which the metabolic defect appears to result in a quantitative, rather than in a qualitative, change in collagen synthesis in vitro will be studied since such cells may highlight regulatory mechanisms that would otherwise be difficult to discern. In another facet of this work, analysis of the effects of heparin on smooth muscle cells will be pursued. The inductive effects of heparin serve as an example of the way in which an extracellular modulator may influence the phenotype of an important vascular cell and may provide an understanding of some of the events leading to atherosclerosis. In sum, these experiments are designed to cover the broad spectrum of regulatory controls that a cell is likely to have at its disposal in modulating extracellular matrix production.